Method and device for charging or discharging a member

ABSTRACT

A method of charging or discharging a member including the steps of, opposing to a member to be acted on, a discharging member having a dielectric member, an inducing electrode and a discharging electrode sandwiching the dielectric member so that the discharging electrode faces the member to be acted on, applying an alternating voltage between the inducing electrode and the discharging electrode to produce a surface discharge on a surface of the dielectric member at the discharging electrode side, wherein a charge density of the surface discharge area is changed in the direction of the width of the discharging electrode, and moving the member to be acted on relative to the discharging electrode to be subjected to a low charge density portion and then to a high charge density portion to charge or discharge the member to be acted on by the thus formed surface discharge.

.Iadd.This application is a continuation-in-part of application Ser. No.193,731 filed May 13, 1988, now abandoned, which was an application forreissue of U.S. Pat. No. 4,589,053. .Iaddend.

BACKBROUND OF THE INVENTION

This invention relates to a method of electrically charging ordischarging a member and a discharging device using the same, which areusable with an electrostatic recording process, an electrophotographyprocess and the like.

In the field of electrophotography and electrostatic recording, coronachargers and dischargers are known and widely used, in which a highvoltage is applied to a fine wire of a diameter 0.1 mm, for example, toproduce corona discharge. However, they involve a drawback that the wireis easily broken because it is thin. Also, the wire is easily stained ordusted, which results in non-uniform corona production, and therefore,non-uniform charging or discharging of a member to be charged ordischarged. In addition, a conductive shield which encloses the coronawire has to be remote therefrom by a certain distance, so that there isa limitation in reducing the size of the device.

Another type of discharger has been proposed, as disclosed in U.S. Pat.No. 4,155,093 corresponding to Japanese Laid-Open Patent Application No.53537/1979, wherein a dielectric member is sandwiched by two electrodes.By applying alternating voltage between the electrodes, positive andnegative ions are produced at the junction between the dielectric memberand one of the electrodes. Of these ions, the ions of a desired polarityare is extracted by an external electric field. This type of dischargeris advantageous in that the size can be much reduced by making thedielectric member thin (not more than 500 microns preferably 20-200microns).

The present invention is intended to further improve the dischargingdevice of this type.

SUMMARY OF THE INVENTION

It is a principal object of the present invention to provide a methodand a device whereby a member to be charged or discharged is subjectedto an increasing charging or discharging power to avoid an abruptcharging operation.

It is another object of the present invention to provide a method and adevice whereby a member to be charged or discharged is substantiallyuniformly charged or discharged.

It is a further object of the present invention to provide a devicewhich is small in size and whereby a member to be charged or dischargedis substantially uniformly charged or discharged.

It is a further object of the present invention to provide a device ofhigh charging or discharging efficiency with a power supply ofrelatively low voltage.

It is a further object of the present invention to provide a method anda device which are stable in operation against variations in ambientconditions, such as the temperature and humidity and whereby a member tobe charged or discharged is satisfactorily uniformly charged ordischarged.

These and other objects, features and advantages of the presentinvention will become more apparent upon a consideration of thefollowing description of the preferred embodiments of the presentinvention taken in conjunction with the accompanying drawings.

According to an embodiment of the present invention, there is provided adevice for charging or discharging a member, comprising, a dielectricmember, an inducing electrode and a discharging electrode sandwichingthe dielectric member, and a power source for applying an alternatingvoltage between the inducing electrode and the discharging electrode toproduce a surface discharge on a surface of the dielectric member at thedischarging electrode side, wherein a charge density of the surfacedischarge area is changed in the direction of width of the dischargingelectrode, and abrupt charging operation can be avoided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a discharging device according to an embodiment of thepresent invention.

FIG. 2 is a perspective view of a discharging member used with thedischarging device shown in FIG. 1.

FIG. 3A shows a state of surface discharge when the present invention isnot used.

FIGS. 3B and 3C show states of surface discharge in the charging ordischarging method and in the discharging device according to anembodiment of the present invention.

FIG. 4 shows a relation between a peak-to-peak value of an alternatingvoltage applied to the discharging device.

FIG. 5 shows a discharging device according to another embodiment of thepresent invention.

FIG. 6A is a perspective view of a discharging member used with thedischarging device shown in FIG. 5.

FIGS. 6B, 6C and 6D show examples of electrically connecting plural rowsof discharging electrodes.

FIG. 7A shows a state of a surface discharge in the discharging deviceof FIGS. 5 and 6.

FIG. 7B shows a state wherein the surface discharge area is totallyuniform along the longitudinal direction.

FIG. 7C shows a state of a surface discharge when the surface dischargeis not sufficient.

FIG. 8 shows another embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1, there is shown a discharging device according tothe present invention, which includes a discharging member 1 opposed toa member 2 to be charged or discharged (hereinafter simply called amember to be charged). The discharging member 1 comprises a dielectricmember 3, an inducing electrode 4 and a discharging electrode 5. FIG. 2is a perspective view of the the discharging member 1. The dischargingelectrode 5 is a single linear elongate member disposed so as to extendparallel to the center of the inducing electrode 4.

Between the inducing electrode 4 and the discharging electrode 5, analternating voltage is applied by alternating voltage applying means 6.On the other hand, the member 2 to be charged which is moved in thedirection of the arrow relative to the discharging device 1, comprises aconductive base member 2a and an insulating or photoconductive member2b. Between the conductive layer 2a and the discharging electrode 5, abias voltage is applied by bias voltage applying means 7.

In operation, when the alternating voltage is applied between theinducing electrode 4 and the discharging electrode 5, an electricdischarging occurs adjacent to the discharging electrode 5 to producesufficient positive and negative ions. Because of the bias voltageapplied between the discharging electrode 5 and the conductive base 2aof the member 2 the positive or negative ions are selectively extractedand directed to the insulating or photoconductive layer 2b surface ofthe member 2 so as to charge it to a desired level in the selectedpolarity.

As for the material of the dielectric member, a relatively high hardnessmaterial, such as ceramics, mica, glass or the like, or a flexibleorganic high polymer, such as polyimide resin, ethylene tetrafluoride,polyester, aclylic material vinyl chloride polyethylene or the like, maybe used.

FIGS. 3A and 3B show states of surface discharge at the dischargingelectrode 5, as seen from the side of the discharging electrode 5, whenthe alternating voltage is applied between the inducing electrode 4 andthe discharging electrode 5 of the discharging device 1 shown in FIGS. 1and 2. In these Figures the inducing electrode 4 contacted to thebackside of the dielectric member 3 is shown by phantom lines. The widththereof is designated by L. The hatched area is the area in which thesurface discharge occurs along the surface of the dielectric member 3 atthe both sides of the discharging electrode 5.

FIG. 3A shows the state of the surface discharge when the presentinvention is not used. The surface discharge area 10 extends from bothlateral sides of the discharging electrode 5, and the width 1 thereof isnot even along the length of the discharging electrode 5. Therefore,when the member 2 to be charged is opposed to the discharging electrode5 and moved relative thereto as shown in FIG. 1 to charge the insulatingor photoconductive layer 2a, the surface thereof is not uniformlycharged, that is, the surface potential distribution is non-uniform inthe longitudinal direction, because of the above-describednon-uniformness.

It has been found that the width 1 of the surface discharge area 10changes with the peak-to-peak value of the alternating voltage appliedbetween the inducing electrode 4 and the discharging electrode 5.

FIG. 4 shows this, the peak-to-peak value vs the width of the surfacedischarge area 10. The surface discharge starts at the a particularpeak-to-peak voltage. With the increase of the peak-to-peak value, thesurface discharge area width increases and finally saturates. Thesurface discharge area width, when saturated, is substantially equal tothe width L of the inducing electrode 4, that is, the surface dischargearea extends substantially as far as the lateral ends of the inducingelectrode 4. It does not extend beyond the lateral ends even if thepeak-to-peak value is further increased. The used dielectric member 3was of alumina ceramics having the thickness of 200 microns, and thedischarging electrode 3 and the inducing electrode 4 were 500 micronswide and 6.5 mm wide, respectively.

The present invention utilizes this to provide a substantially uniformcharging of the member 2 to be charged over the entire length of thedischarging device 1, independently of the non-uniformness of thedielectric member 3 material and/or the score of the electrodes andothers.

FIG. 3B shows the present invention. As shown, the discharging electrode5 is parallel with the center line of inducing electrode 4, butdisplaced toward one of the lateral ends of inducing electrode 4 (inthis Figure, toward the upper end). Therefore, the distance from thedischarging electrode 5 is smaller to said one of the lateral ends thanto the other end, of the inducing electrode 4 (the lower end). Becauseof this displacement, the upper boundary 12 of surface discharge area 10comes closer to the upper lateral end of inducing electrode 4, but itsaturates at the upper lateral end, and it does not extend beyond thelateral end, as will be understood from the explanation with FIG. 4.Thus, the upper boundary of surface discharge area 10 is substantiallyrectilinear over the entire length of the discharging member 1, and theion density within the upper part of the surface discharge area isuniform over the length thereof. The lower boundary of surface dischargearea 10 remains non-uniform. However, by moving member 2 under thedischarging member 1 as shown in FIG. 1 in the direction of arrow so thethat the member 2 is first subjected to the ions of the lower part (FIG.3B) and then subjected to the upper part thereof, the influence of thenon-uniformness at the lower part is reduced by the uniform dischargingarea of the upper part, so that a substantially uniform charging can beeffected. This arrangement corresponds to displacing the dischargingelectrode 5 rightwardly in FIG. 1 from the center of the inducingelectrode 4.

Another important advantage will next be explained. Where thedischarging electrode 5 is displaced as shown in FIG. 3B, for example,the upper surface discharge area has a higher charge density than thelower part. Therefore, when member 2 is moved in the direction describedabove, the member 2 is subjected, during the first half, to relativelyweak charging operation and is then subjected, during the last half, torelatively strong charging operation with the high charge densitysurface discharge area so as to be charged to a desired level.

A photosenitive member, for example, should not abruptly be charged upto a high level, since then the service life thereof is shortened, or apin hole can be formed therein. This is well-known. The presentinvention is highly advantageous for the purpose of such use, since thefirst half of the charging operation is with the weaker charging powder,and the last half can be sufficiently strong to charge it up to thedesired level within a limited period of time.

It has been found that the lower boundary 13 of the surface dischargearea 10 can be extended to the lower lateral end of inducing electrode 4by raising the peak-to-peak value of the alternating voltage appliedbetween the inducing electrode 4 and the discharging electrode 5. Withthe increase of the peak-to-peak value, the lower boundary 13 of thesurface discharge area expands toward the lower lateral end of inducingelectrode 4 and finally saturates. The lower boundary 13, whensaturated, reaches substantially to the lower lateral end of theinducing electrode 4. It does not expand beyond the lateral end even ifthe peak-to-peak value is further increased. The present inventionutilizes this to make uniform the surface discharge area width over theentire length of the discharging device 1, independently of thenon-uniformness of the dielectric member 3 material and/or the score ofthe electrodes and others. Additionally, rapid or sudden charging can beavoided.

FIG. 3C shows the surface discharge 10 of the discharging device of thepresent invention using this phenomenon. The peak-to-peak value of thealternating voltage is so selected as to extend both of the lateral endsof the surface discharge area substantially to the respective lateralends of the inducing electrode 4 over the entire length of thedischarging device 1. Then, as shown in FIG. 3C, the width of thesurface discharge area 10 is substantially equal to the width of theinducing electrode 4 and therefore uniform. Since the applied voltage isalternating, the width, very strictly speaking, changes at a highfrequency, but the maximum width is substantially equal to the width ofthe inducing electrode 4 and is uniform.

When the member 2 to be charged is subjected to the charging operationin the manner shown in FIG. 1 with the above described discharger, themember 2 to be charged is further uniformly charged. As described above,the surface discharge area 10 does not extend beyond the width L of theinducing electrode 4, even if the voltage is increased. The only changeis the increase of the charge density in the surface discharge area 10.The charge densities within the upper and lower surface discharge areasare respectively uniform in the longitudinal direction. Since the chargedensity at the upper surface discharge area is higher than that of thelower discharge area, abrupt charging operation can be avoided similarlyto FIG. 3B embodiment.

By using this phenomenon to the maximum extent, a charging can be maderelatively stable against the change in ambient conditions so that asatisfactory charging can be effected.

As described above, according to the present invention, the small sizedischarger is improved in its non-uniformness of the charging. And,without the necessity of use of a special control means, the member tobe charged or discharged can be firstly acted on weakly and then actedon strongly up to a desired level.

The dielectric member 3 of alumina ceramics having the thickness of 200microns was sandwiched by the discharging electrode 5 having the widthof 500 microns and the inducing electrode 4 having the width of 4 mm.The discharging electrode 5 was displaced by 1 mm toward one of lateralends (upper end in FIG. 3B) of the inducing electrode 4, from the centerthereof. Between the discharging electrode 5 and the inducing electrode4, an alternating voltage having the peak-to-peak value of 2 KVpp wasapplied. The surface discharge area did not extend to the lateral endsof the inducing electrode 4. When the member 2 to be charged wassubjected to the discharging member 1 with the output of the biasvoltage by the bias source 7 being 2 KV, the non-uniformity of plus andminus 8% was measured on the surface of the member 2.

Then, the alternating voltage was increased up to 3 KVpp to extend theupper end of the surface discharage area 10 substantially to the upperlateral end of the inducing electrode 4, and the charging was carriedout under the same conditions. The measured non-uniformity was plus andminus 4.5%. Further, the alternating voltage is raised up to 5 KVpp toextend both lateral ends of the surface discharge area to the respectivelateral ends of the inducing electrode over the entire length. Themeasured non-uniformity was plus and minus 3%.

According to the present invention, the non-uniformity of charging canbe reduced as described above, and in addition, the abrupt charging canbe avoided.

FIGS. 5 and 6A show a discharging device according to another embodimentof the present invention. FIG. 6A is a perspective view of thedischarging member 1. Since this embodiment is similar to the embodimentdescribed with FIGS. 1 and 2, except that the discharging electrode 5 iscomprised of plural rows of discharging electrode members disposed atthe intervals which will be described in detail hereinafter, and thatthe width of the inducing electrode 4 is correspondingly larger, thedetailed description of the similar parts is ommited for the sake ofsimplicity by assigning the same reference numerals to the elementshaving the corresponding functions.

FIG. 7A shows the embodiment but it has four discharging electrodemember 5a, 5b, 5c and 5d. The topmost discharging electrode member 5aand the bottommost discharging electrode member 5d are so disposed thatthe distance L0 between the topmost discharging electrode member 5a andthe upper lateral end of inducing electrode 4 is smaller than thedistance L4 between the bottommost discharging electrode member 5 andthe lower end of inducing electrode 4.

The upper boundary 12 of the surface discharge area 10a of the topmostelectrode member 5a reaches substantially to the upper lateral ends ofthe inducing electrode 4. Therefore, the upper boundary 12 of thesurface discharge area 10a is substantially rectilinear along thedischarging member 1. And, the ion density within this area is uniformalong the length thereof. However, because of the above-describeddimensional conditions, the lower boundary 13 of the surface dischargearea 10d is not uniform.

It is preferable that the distance L1, L2 and L3 between adjacentelectrode members increase toward the lower part in FIG. 7A, that is,L1<L2<L3 . . . Ln. Further, it is preferable that the distance L0between the upper lateral end of the inducing electrode and the topmostdischarging electrode member 5a is smaller than one half of the distanceL1 between the topmost electrode member 5a and the adjacent electrodemember 5b, and that the distance L4 between the lower lateral end of theinducing electrode 4 and the bottommost discharging electrode member 5ais larger than one half of the distance L3 between the bottommostelectrode member 5d and the adjacent electrode member 5c, namely,L0<(1/2)L1, and L4>(1/2)L3.

Since the distances between the adjacent electrode members 5a, 5b, 5cand 5d are so related as described above, the lower boundary of thesurface discharge 10a is partially contacted or superposed with theupper part of the surface discharge area extending from the dischargeelectrode member 5b. However, they are apart at some portions so thatthey are generally non-uniform. Between the electrode members 5b and 5c,and between the electrode member 5c and 5d, the surface discharge areasare spaced further apart. However, the upper boundary 12 of the surfacedischarge area 10a is substantially coincident with the upper lateralend of the inducing electrode 4 and is substantially rectilinear, andthe ion density is uniform along the length of the discharging member 1,whereby, if the member 2 to be charged is opposed to the dischargingmember 1 and is moved relative thereto so as to first be subjected tothe lower surface discharge area 10d of the discharging member 1 andthen to the upper surface discharge area 10c, 10b and 10a in this order,the influence of the nonuniformity of the surface discharge area isremoved by this final surface discharge area 10a, so that asubstantially uniform charging is provided.

As in the previous embodiment, the charge density in the surfacedischarge area 10a is higher than that of the lower surface dischargeareas, which gradually decreases toward the lower part in the Figure.Therefore, when the member 2 to be charged is moved in theabove-described direction, it is first subjected to a relatively weakcharging with the lower charge density, and the charging power isgradually increased until it is charged to a desired level by thehighest charge density surface discharge area.

As described hereinbefore, this is particularly advantageous in anelectrophotographic process or the like.

The plural rows of electrode members may be electrically connected inthe fashion of a comb as shown in FIG. 6B; connected at opposite ends asshown in FIG. 6C; or connected in a zig-zag fashion as shown in FIG. 6D.

Where plural electrode members are used, the intervals between adjacentones are preferably monotonously decreased as described above. However,when the number thereof is large, it is not necessary that they decreasemonotonously in the strict sense, if they are generally decreasing.

By raising the peak-to-peak value of the alternating voltage appliedbetween the inducing electrode 4 and the discharging electrode 5, thewidth of the surface discharge area extending from each of thedischarging electrode members increases, until the surface dischargeoccurs over the entire width of the inducing electrode 4.

FIG. 7B shows such a state. In this embodiment, the peak-to-peak voltageof the alternating voltage is such that both sides of the surfacedischarge area are substantially coincident of the respective lateralends of the inducing electrode 4, and such that there is no missing partof the surface discharge between the electrode members 5a, 5b, 5c and5d. As shown, both of the lateral sides of the entire surface dischargearea extend substantially to the respective lateral sides of theinducing electrode 4 so that the surface discharge area is totallyuniform along the longitudinal direction.

When the member 2 to be charged is subjected to the charging operationin the manner shown in FIG. 1 with the above described discharger, themember 2 to be charged is further uniformly charged. As described above,the surface discharge area does not extend beyond the width L of theinducing electrode 4, even if the voltage is increased. The only changeis the increase of the charge density in the surface discharge area 10.The charge density is uniform along the length of the entire dischargingmember 1 at a given position in width direction. Additionally, thecharge density gradually increases from one lateral end to anotherlateral end, so that it is advantageous when used with anelectrophotography process since abrupt charging can be avoided, as inthe case of FIG. 3B.

By using this phenomenon to the maximum extent, a charging can be maderelatively stable against the charge in ambient conditions so that asatisfactory charging can be effected.

When the discharging electrode is comprised by a single electrodemember, the surface discharge area width is determined by thepeak-to-peak value of the alternating voltage. Therefore, in order toincrease the width of the surface discharge area, it is necessary toraise the voltage to a relatively great extent. Where, however, aplurality of electrode members are used, the width can be increasedwithout the necessity of raising the voltage to such an extent. Thewidth can be increased as desired by increasing the number of theelectrode members, thus remarkably enhancing the charging or dischargingefficiency. Further, by changing the intervals between the electrodemembers, the charge density distribution can be changed.

FIG. 7C illustrates the state of the surface discharge which isdifferent from those described above. In this Figure, the surfacedischarge areas 10a, 10b, 10c and 10d extend from the respectivedischarge electrode members 5a, 5b, 5c and 5d, and the width of each ofthem is non-uniform along the length. So, if the member 2 to be chargedis moved as shown in FIG. 1 to charge the surface of the insulating orphotoconductive layer 2b, the distribution of the resultant charging isnot uniform along the length of the discharging member 1 as in FIG. 3A.

The dielectric member 3 of alumina ceramics having the thickness of 200microns was sandwiched by the inducing electrode 4 having the width of16 mm and four discharging electrode members 5a, 5b, 5c and 5d spaced by1 mm(L0), 3 mm(L1), 4 mm (L2), 5 mm (L3) and 3 mm (L4), respectively,and each having the width of 500 microns. Between the dischargingelectrode members and the inducing electrode 4, an alternating voltagehaving the peak-to-peak value of 2 KVpp was applied. The surfacedischarge area did not extend to the lateral ends of the inducingelectrode 4, as in FIG. 7C. When the member 2 to be charged wassubjected to the discharging member 1 with the output of the biasvoltage by the bias source 7 being 2 KV, the non-uniformness of plus andminus 7.5% was measured on the surface of the member 2.

Then, the alternating voltage was increased up to 3 KVpp to extend atleast the surface discharage area 10a of the topmost electrode member 5asubstantially to the upper lateral end of the inducing electrode 4, andthe charging was carried out under the same conditions. The measurednon-uniformness was plus and minus 4%. Further, the alternating voltageis raised up to 5 KVpp to extend the surface discharge areas to coverthe entire area corresponding to the inducing electrode 4. The measurednon-uniformness was plus and minus 2.5%.

According to the present invention, the non-uniformness of charging canbe reduced as described above, and in addition, the abrupt charging canbe avoided.

As for other alternatives for effecting the gradual increase of thecharging power, the thickness of the dielectric member 3 may be changedin the direction of the width as shown in FIG. 8. In this structure, theelectric field around the discharging electrode 5 is stronger with thedecrease of the dielectric member 3 thickness, the surface dischargearea extends more to the thin dielectric member side. The dischargingelectrode 5 may be comprised by plural rows of discharging electrodemembers. In this embodiment, the thickness charges continuously, but itmay be changed stepwisely.

Alternatively, where plural discharging electrode members are used, thevoltage applied thereto may be changed gradually.

As described above, according to the present invention, the member to becharged or discharged can be first charged with a weak charging powerand then charged with an increasing charging power without the necessityof using a special control means, and in addition the substantiallyuniform charging can be achieved in the small-sized discharging device.

In each of the above-described embodiments, surface discharge area width1 is dependent on the material, dielectric constant and the surfaceresistivity of the dielectric member 3, but person with ordinary skillin the art can determine the peak-to-peak value in accordance with thosefactors without difficulty.

Also, the width varies in dependence on the ambient conditions, such asatmospheric pressure, temperature, humidity and the degree of stain ofthe dielectric member 3 surface. The peak-to-peak value can be sodetermined, based on the actual conditions under which the device isused, that the surface discharge area 10 extends substantially to thelateral ends of the inducing electrode 4, and such determination isdesirable.

The alternating voltage is not limited to a usual AC voltage, and may berectangular wave voltage or pulse alternating voltage.

The foregoing explanation has been made with respect to the charging ofa member. Where the discharging device is placed closer to the member,the member can be discharged, that is, an electric charge can be removedfrom the member. In this case, the voltage source 7 is not necessary.The present invention described is usable, and the advantages thereofcan be provided, also in this case.

The voltage source 7, when used, may supply a DC voltage or pulsatingvoltage if the ions generated near the discharging electrode 5 can bedirected to the member to be charged or discharged. While the inventionhas been described with reference to the structures disclosed herein, itis not confined to the details set forth and this application isintended to cover such modifications or changes as may come within thepurposes of the improvements or the scope of the following claims.

What is claimed is:
 1. A method of charging or discharging a membercomprising the steps of:opposing a discharging member to a member to beacted on, said discharging member having a dielectric member, and havingan inducing electrode and a discharging electrode sandwiching thedielectric member so that the discharging electrode faces the member tobe acted on, wherein the discharging electrode extends on a surface ofthe dielectric member parallel to a center line of the inducingelectrode at such a position that the discharging electrode is spacedaway from one lateral end of the inducing electrode by a smallerdistance than from the other lateral end of the inducing electrode;applying an alternating voltage between the inducing electrode and thedischarging electrode to product a surface discharge area on a surfaceof the dielectric member at the discharging electrode side, wherein oneof the lateral ends of the surface discharge area is substantiallycoincident with said one of the lateral ends of the inducing electrode;and moving the member to be acted on relative to the dischargingelectrode to charge or discharge the member to be acted on by the thusformed surface discharge.
 2. A device for charging or discharging amember, comprising:a dielectric member; an inducing electrode and adischarging electrode sandwiching said dielectric member, wherein thedischarging electrode extends on a surface of the dielectric memberalong a center line of the inducing electrode at such a position thatthe discharging electrode is spaced away from one lateral end of theinducing electrode by a smaller distance than from the other lateral endof the inducing electrode; and a power source for applying analternating voltage between said inducing electrode and said dischargingelectrode to produce a surface discharge on a surface of the dielectricmember at the discharging electrode side, wherein one of the lateralends of the surface discharge area is substantially coincident with saidone of the lateral ends of the inducting electrode.
 3. A deviceaccording to claim 2, wherein said discharging electrode has plural rowsof discharging electrode members, and wherein a distance between saidone of the lateral ends of said dielectric member and a row of thedischarging electrode members which is closest to said one lateral endis smaller than a distance between said other lateral end of saiddielectric member and a row of the discharging electrode members whichis closest to said other lateral end.
 4. A device according to claim 3,wherein distances between adjacent rows of electrode members decreasestoward said one of the lateral ends.
 5. A method of charging ordischarging a member comprising the steps of:opposing a dischargingmember to a member to be acted on, said discharging member having adielectric member, and having an inducing electrode and a dischargingelectrode sandwiching the dielectric member so that the dischargingelectrode faces the member to be acted on, wherein the dischargingelectrode extends on a surface of the dielectric member along a centerline of the inducing electrode at such a position that the dischargingelectrode is spaced away from one lateral end of the inducing electrodeby a smaller distance than from the other lateral end of the inducingelectrode; applying an alternating voltage between the inducingelectrode and the discharging electrode to produce a surface dischargeon a surface of the dielectric member at the discharging electrode side,wherein a charge density adjacent said one of the lateral ends of theinducing electrode is higher than that adjacent said other end thereof;and moving the member to be acted on relative to the dischargingelectrode to charge or discharge the member to be acted on by the thusformed surface discharge.
 6. A method of charging or discharging amember comprising the steps of:opposing a discharging member to a memberto be acted on, said discharging member having a dielectric member andhaving an inducing electrode and a discharging electrode sandwiching thedielectric member so that the discharging electrode faces the member tobe acted on, wherein the discharging electrode extends on a surface ofthe dielectric member along a center line of the inducing electrode andwherein the dielectric member has a thickness increasing in a directionfrom one lateral end of the inducing electrode to the other lateral endthereof; applying an alternating voltage between the inducing electrodeand the discharging electrode to produce a surface discharge on asurface of the dielectric member at the discharging electrode side,wherein a charge density adjacent said one lateral end of the inducingelectrode is higher than that adjacent said other end thereof; andmoving the member to be acted on relative to the discharging electrodeto charge or discharge the member to be acted on by the thus formedsurface discharge.
 7. A method of charging or discharging a membercomprising the steps of:opposing a discharging member to a member to beacted on, said discharging member having a dielectric member and havingan inducing electrode and a discharging electrode sandwiching thedielectric member so that the discharging electrode faces the member tobe acted on, wherein the discharging electrode extends on a surface ofthe dielectric member along a center line of the inducing electrode andwherein the dielectric member has a thickness increasing in a directionfrom one lateral end of the inducing electrode to the other lateral endthereof; applying an alternating voltage between the inducing electrodeand the discharging electrode to produce a surface discharge on asurface of the dielectric member at the discharging electrode side,wherein one of the lateral ends of the surface discharge area issubstantially coincident with said one lateral end of the inducingelectrode; and moving the member to be acted on relative to thedischarging electrode to charge or discharge the member to be acted onby the thus formed surface discharge.
 8. A method according to claims 1,5, 6 or 7, further comprising the step of forming a bias electric fieldbetween the discharging electrode and said member to be acted on to moveions produced by the surface discharge, said field being formed with apredetermined polarity with respect to the member to be acted on.
 9. Amethod according to claim 6 or 7, wherein the thickness of thedielectric member increases continuously.
 10. A method according toclaims 6 or 7, wherein the thickness of the dielectric member increasesin steps.
 11. A device for charging or discharging a member,comprising:a dielectric member; an inducing electrode and a dischargingelectrode sandwiching said dielectric member, wherein the dischargingelectrode extends on a surface of the dielectric member along a centerline of the inducing electrode at such a position that the dischargingelectrode is away from one lateral end of the inducing electrode by asmaller distance than from the other lateral end of the inducingelectrode; and a power source for applying an alternating voltagebetween said inducing electrode and said discharging electrode toproduce a surface discharge on a surface of the dielectric member at thedischarging electrode side, wherein a charge density adjacent said onelateral end of the inducing electrode is higher than that adjacent saidother end thereof.
 12. A device for charging or discharging a member,comprising:a dielectric member; an inducing electrode and a dischargingelectrode sandwiching said dielectric member, wherein the dischargingelectrode extends on a surface of the dielectric member along a centerline of the inducting electrode and wherein said dielectric member has athickness increasing in a direction from one lateral end of the inducingelectrode to the other lateral end of the inducing electrode; and apower source for applying an alternating voltage between said inducingelectrode and said discharging electrode to produce a surface dischargeon a surface of the dielectric member at the discharging electrode side,wherein a charge density adjacent said one lateral end of the inducingelectrode is higher than that adjacent said other end thereof.
 13. Adevice for charging or discharging a member, comprising:a dielectricmember; an inducing electrode and a discharging electrode sandwichingsaid dielectric member, wherein the discharging electrode extends on asurface of the dielectric member along a center line of the inducingelectrode and wherein said dielectric member has a thickness increasingin a direction from one lateral end of the inducing electrode to theother end of the inducing electrode; and a power source for applying analternating voltage between said inducing electrode and said dischargingelectrode to produce a surface discharge on a surface of the dielectricmember at the discharging electrode side, wherein one of the lateralends of the surface discharge area is substantially coincident with saidone of the lateral ends of the inducting electrode.
 14. A deviceaccording to claims 2, 11, 12 or 13, further comprising means forapplying a bias electric field between the discharging electrode and themember to be acted on to move ions produced by the surface discharge,said field having a predetermined polarity with respect to the member tobe acted on.
 15. A device according to claims 12 or 13, wherein thethickness of the dielectric member increases continuously.
 16. A deviceaccording to claims 12 or 13, wherein the thickness of the dielectricmember increases in steps.